Issue #3423

Adding a CodeMirror option for controlling how long the ternTooltip should be visible before closing

... and export (via defineExtension) a method to explicitly trigger
linting from user code.

Closes #3409

See http://discuss.codemirror.net/t/tern-webworker-causing-hint-flickering/300

Issue #3337

Issue #3337
Issue #3338

Tern completion for required module returns name (module wuith quote)
and displayName (module without quote). This PR gives the capability
to display completion for required module without quote.

I noticed that the image that accompanies auto-completion suggestions
when the tern addon is active gets cut slightly, because the default
line height is slightly smaller than the image height.

This change above ensures that the line height is bigger, hence
ensuring that the image is fully shown.

See http://discuss.codemirror.net/t/tern-special-characters-causing-issues/294

This PR initialize docs before creating tern server instance, because
in some case, tern server creation call getFile which use docs.

I have this case by using requirejs tern plugin + custom plugin which
defines modules :

```json
{
    "!name": "delite",
    "!define": {
      "!requirejs": {
        "delite/register": {
          "!type": "fn(tag: string, superclasses: [], props: ?) -> fn()",
      }
    }
  }
```

Issue #3308

Issue #3243

Closes #3233

Issue #3229

This makes it impossible to change the mode of the editor
and still automatically get appropriate annotations.

Issue #3227

Issue #3189

Fixes https://github.com/codemirror/CodeMirror/issues/3215

Issue #3204

And change handlebars demo to use it.

Clean up duplicated logic

Issue #3189

Issue #3173

Closes #3178